Changing image in header bar

Hi. I am trying to change the image next to the Page Title on my pages to make it more unique to the page, Instead of a “server”.

http://rippabusinesswebhosting.com.au/blog-2/ (remove space)

As you can see on this page, Next to the header “Blog” on the black strip there is a picture of the “server”. In which file would i edit this.

Hope you can help